Figure 2. Molecular cytogenetic probes. (a) Normal human metaphase spread showing hybridization of the centromeric region of chromosomes 7 (green) and 8 (red) using α-satellite probes. Chromosomes counterstained in blue using DAPI. (b) Human male metaphase spread with deletion of the elastin (ELN) locus at the Williams syndrome critical region near the centromere on one homologue of chromosome 7. Cosmid probe for the ELN locus and a control probe are visible on the normal homologue (right); however, only the control probe can be seen on the deleted homologue (left). (c) Normal human metaphase spread with whole-chromosome paint probe for chromosome pair number 15 in red. (d) Cross-species colour banding (RX-FISH®) on normal human male chromosomes arranged in standard karyotype format.